The long-term focus of our work is cell division in bacteria. In particular, we are interested in how the division septum is formed, and how its formation is coordinated with other events in the cell- cycle such as chromosome segregation. An ancillary objective is to understand how proteins are localized to specific subcellular sites. This interest stems from the observation that many proteins involved in septum assembly are localized to the division site. Cell division and protein localization are fundamental cellular processes of importance to all organisms, including humans, and underlie diseases such as cancer, but are often difficult to study due to technical limitations. The wealth of genetic tools available in Escherichia coli makes this an ideal model organism for studies of basic cellular processes. Septum assembly in E. coli requires at least nine essential proteins, all of which localize to the division site. Our hypothesis is that these proteins form of complex that contains all of the activities need for septum assembly, and that interactions among these proteins are important for their recruitment to the division site and for regulating their activities. Thus, we want to know more about the detailed function of these proteins, to identify interactions among these proteins, and to know whether the set is complete. To approach these issues we will characterize FtsI, a membrane protein with an enzymatic activity (transpeptidase) related to peptidoglycan synthesis. Specifically, we will (i) use a combination of genetics and fluorescence microscopy to identify sequences in FtsI that target this protein to the division site; (ii) use biochemical and genetic approaches to look for proteins that interact directly with FtsI; and (iii) use fluorescence microscopy to determine the subcellular location of three transglycosylases postulated to be involved in synthesis of septal peptidoglycan and to interact with FtsI. A better understanding of cell division in a simple bacterial system might shed light on these processes in other organisms, including humans. In addition, a better understanding of these processes might lead to more knowledge-based approaches to developing new antibiotics. In this regard, it is worth noting that four of the proteins to be studied here (FtsI and the three transglycosylases) are primary targets of beta-lactam antibiotics.